The present invention relates to a rail mounting assembly and, more particularly, to a rail mounting assembly of the type in which a metal frame is connected with the rail support platform by a body of an elastomer.
Rail mounting assemblies in which the rail is supported on a suitable surface with an elastomeric material between a top plate and a frame and in which the elastomer is bonded to the top plate and the frame are known. However, in such assemblies, generally speaking the elastomer is subjected to cycles of compression and tension which cause deterioration of the elastomer or separation of the elastomer from the metal surfaces. Prior constructions, moreover, were prone to deterioration from poor ratios of dynamic to static stiffness, force distribution, unsatisfactory lateral to vertical stiffness, failure to minimize strain, fatigue failure, corrosion and were frequently unsatisfactory with respect to thermal contraction and expansion, and the ability for foreign material to collect in the unit or combinations thereof.
It is, therefore, the principal object of the invention to provide an improved rail mounting assembly whereby the drawbacks of earlier devices are avoided.
Another object of this invention is to provide an improved rail mounting assembly which is less susceptible to corrosion, is less affected by cyclic compression and tension and does not tend to collect foreign matter.
An important object is to provide a mounting assembly which has a unique ability to control the extent of transfer of forces at specific or desired locations, has a lower dynamic to static stiffness ratio, has reduced internal strain levels, and has improved resistance to under-bond corrosion.
These objects and others which will become apparent hereinafter are attained, in accordance with the invention, in a rail mounting assembly which comprises:
an elongated metal frame having a generally planar bottom surface adapted to rest upon a support, a pair of outwardly convex curved end members and a pair of mutually parallel longitudinal members, the members surrounding an opening of the frame, the end members having downwardly and inwardly inclined flanks delimiting the opening, the longitudinal members having flanks generally perpendicular to the bottom surface delimiting the opening;
an elongated top plate received in the opening in the frame and having an upper surface forming a platform for receiving a rail and formations flanking the platform for securing the rail on the platform, the top plate having a pair of outwardly convex curved ends spacedly juxtaposed with the end members and a pair of longitudinal sides spacedly juxtaposed with the longitudinal members, the ends having downwardly and inwardly inclined flanks forming respective gaps widening upwardly and downwardly with the downwardly and inwardly inclined flanks of the end members, the longitudinal sides having flanks defining respective gaps with the flanks of the longitudinal members; and
a body of an elastomer received in the gaps, bonded to and fully covering the flanks and resiliently holding the frame and top plate together.
Advantageously, the elastomer in the gaps between the flanks along the longitudinal sides has downwardly open crevices extending the full lengths of the longitudinal sides which can close under load. These crevices can be narrower toward the ends of the longitudinal sides than at middle portions thereof.
The crevices or voids permit the distribution of the load or stress to maximize performance and durability.
According to another feature of the invention, the elastomer extends over the rounded tops of the ends of the top plate and into a trough or valley formed between each end and the rail receiving platform or the formations for securing the rail thereto.
The elastomer can also extend over the rounded edges of the frame members at the ends of the frame.
The system of the invention has numerous advantages of prior art systems. For example, by varying the thickness and configuration of the voids or crevices in the body of the elastomer, the transfer of longitudinal forces can be controlled between zero and an undiminished level. The variable thickness and configuration of the voids also permits controlling the amount of force transferred from the top plate to the frame at any location as desired.
Since, with the present invention, the ends of the top plate and the frame are encapsulated at least where the two are juxtaposed, the danger of corrosion between the elastomer and the metal surface at each location is limited. While corrosion can occur where the metal is exposed beyond the elastomer, this corrosion is sufficiently far from the active rubber under cyclic stress to reduce the risk of deterioration of the bonded surfaces.
The elastomer body of the invention lies essentially in a single horizontal plane and thus insures an effective seal which represents a significant advance over earlier bonded rail mounting systems. The curvature at the ends of the top plate and frame has been found to be significant as well in maximizing lateral stability and minimizing stress in the elastomer, thereby also maximizing the life of the mount. The curved end faces insure a large volume of elastomer between the end surfaces even with a minimum width of the frame and can contribute to the self centering properties of the mount.